1. Field of the Invention
The present invention relates to a head positioning control method of a disk apparatus, head positioning control device and disk apparatus, and more particularly to a head positioning control method, head positioning control device and disk apparatus for suppressing position shift caused by external vibration.
2. Description of the Related Art
It is important for a disk device, such as a magnetic disk device or optical disk device, to accurately position the head on the target track in order to improve recording density.
For this positioning control, an eccentricity correction method using an eccentricity estimation observer has been proposed to handle the eccentricity of a disk (e.g. Japanese Patent Application Laid-Open No. H7-50075 and No. 2000-21104).
Such an eccentricity estimation observer calculates a control value of an actuator from an error between an actual position error and estimated position error, using state estimation gains A, B, C, F and L, and calculates the state quality (position, velocity, bias value, eccentricity) of the next sample.
Here the estimated gain L consists of an estimated position gain L1, estimated velocity gain L2, estimated bias gain L3 and estimated eccentricity gains L4 and L5. And L1, L2 and L3 show the characteristics of the controller itself, and L4 and L5 show the response characteristics to eccentricity, which is a periodic disturbance.
By using such an observer, it is desirable to position control so as to follow up to an external vibration, other than an eccentricity component. In other words, as the recording density of a disk device increases, it is becoming difficult to ignore the influence of external vibration on the positioning accuracy of the head. Also as the use of disk devices expends, disk devices are now also installed on mobile equipment, such as portable terminals, portable telephones and portable AV (Audio/Visual) equipment, therefore adapting a wide range of disturbance frequencies is also demanded.
The follow up performance to disturbances can be increased by increasing the estimated gain using prior art, but in this case, the width of the disturbance suppression range must be widened. If the width of the disturbance suppression range is widened, however, the disturbance model and the original model of the controller interfere each other, thereby changing the control characteristics.